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Objectives: To compare liquid stored and frozen semen using either an Ovsynch or a Cosynch protocol for the first TAI in a 2 x 2 factorial design.
Methods: This experiment was performed on 9 commercial dairy farms in Mecklenburg-Vorpommern, Germany from April 2016 to October 2016. Lactating dairy cows (n = 1,724; 540 primiparous, 1,185 multiparous) were randomly assigned to 1 of 2 synchronization protocols on a weekly basis to facilitate first postpartum timed AI (i.e., Ovsynch-56 or Cosynch-56). Cows were inseminated either 12 to 16 h after the second GnRH injection (Ovsynch-56) or concurrently with the second GnRH injection (Cosynch-56). In addition, 2 different preservation methods for semen were used, i.e. liquid stored semen (10 x 106 sperm/ straw) and frozen semen (20 x 106 sperm/ straw). The type of semen used for TAI changed every other week on each farm (i.e., week 1: frozen semen; week 2: liquid stored semen; week 3: frozen semen). The analysis of P/AI at first TAI was performed by logistic regression using the GENLINMIXED procedure of SPSS.
Results: There was an overall effect of semen preservation method on P/AI with liquid stored semen achieving greater P/AI than frozen semen (29.9 % vs. 24.0 %; P = 0.034). In addition, parity affected P/AI with primiparous having a greater P/AI than multiparous cows (34.8 % vs. 20.2 %; P = 0.001). There was also an effect of TAI protocol on P/AI with cows inseminated in the Ovsynch-56 protocol achieving greater P/AI than cows inseminated in the Cosynch-56 protocol (30.4 % vs. 23.6 %; P = 0.021). Sire had no effect on P/AI (P = 0.899). The effect of semen preservation method differed by TAI protocol. Cows inseminated with liquid stored semen using Cosynch-56 achieved greater P/AI than cows inseminated with frozen semen using the same synchronization protocol (20.0 % vs. 27.5 %; P = 0.032). There was no effect of semen preservation method (liquid stored semen 32.3 % vs. frozen semen 28.6 %; P = 0.330) when cows were inseminated approximately 16 h after GnRH2 injection (Ovsynch-56).
Conclusions: Liquid stored semen achieved greater P/AI in a TAI protocol with a long time interval between insemination and ovulation (Cosynch-56) compared to frozen semen indicating that liquid stored semen might have a longer viability in the reproductive tract compared to frozen semen. Further studies are required to compare fertility of liquid stored semen and frozen semen in cows with inseminations after spontaneous heat.